Variation in gene expression within clones of the earthworm Dendrobaena octaedra

1University of Jyvaskyla, Department of Biological and Environmental Science, University of Jyvaskyla, Jyvaskyla, Finland2University of Oulu, Department of Ecology, University of Oulu, Oulu, Finland3University of Jyvaskyla, Department of Mathematics and Statistics, University of Jyvaskyla, Jyvaskyla, Finland

Abstract

Gene expression is highly plastic, which can help organisms to both acclimate and adapt to
changing environments. Possible variation in gene expression among individuals with the
same genotype (among clones) is not widely considered, even though it could impact the
results of studies that focus on gene expression phenotypes, for example studies using
clonal lines. We examined the extent of within and between clone variation in gene expression
in the earthworm Dendrobaena octaedra, which reproduces through apomictic parthenogenesis.
Five microsatellite markers were developed and used to confirm that offspring
are genetic clones of their parent. After that, expression of 12 genes was measured from
five individuals each from six clonal lines after exposure to copper contaminated soil. Variation
in gene expression was higher over all genotypes than within genotypes, as initially
assumed. A subset of the genes was also examined in the offspring of exposed individuals
in two of the clonal lines. In this case, variation in gene expression within genotypes was as
high as that observed over all genotypes. One gene in particular (chymotrypsin inhibitor)
also showed significant differences in the expression levels among genetically identical individuals.
Gene expression can vary considerably, and the extent of variation may depend on
the genotypes and genes studied. Ensuring a large sample, with many different genotypes,
is critical in studies comparing gene expression phenotypes. Researchers should be especially
cautious inferring gene expression phenotypes when using only a single clonal or
inbred line, since the results might be specific to only certain genotypes.

This work was supported by the Maj and Tor Nessling Foundation (project number 2015038) and the Doctoral Programme in Biological and Environmental Science at University of Jyväskylä.

Dataset Reference:

Microsatellite sequences for Dendrobaena octaedra are in GenBank (BankIt1871234: DO1 KU160480, DO2 KU160481, DO3 KU160482, DO4 KU160483, DO6 KU160484). The transcripts from which we have designed the primers are the property of Dr. Martin Holmstrup and we are not at liberty to submit them to a public database. Transcripts are available on request from Dr. Martin Holmstrup (Aarhus University, Vejsovej 25, building B3.16, 8600 Silkeborg, Denmark. Email: martin.holmstrup@bios.au.dk, phone: +4587158823).